1. Field of the Invention
The present invention relates generally to a sealing system to be mounted on radial bearing-type ball and roller bearings, and more particularly to the construction of a sealing device designed to be fitted inside those bearings.
2. Description of the Prior Art
Conventionally, a ball bearing or roller bearing of the type referred to above usually includes an inner race and an outer race, either of which contains a sealing device that can be fitted and secured in position therein by making use of its elastic rubber property. For the conventional sealing system, when the turning torque that may occur during the lip sliding motion becomes greater than the slip torque that may occur in the area where the sealing device is fitted, the sealing device will rotate with the bearing shaft supported by the bearing. In order to prevent the sealing device from rotating with the bearing shaft in such situation, a greater interference must be provided for the rubber in the space between the sealing device and the inner or outer race where it is fitted. When the greater interference is provided, however, the sealing device may be mounted improperly within the inner or outer race, causing it to lose its ability to engage the race. Part of the rubber in the greater interference may also get out of the inner or outer race, and may suffer damage when the sealing device is fitted in. The result is a defective mounting.
As an alternative solution that addresses the above problem, a sealing plate that provides a different fitting construction has been proposed as disclosed in Japanese Utility Model Registration application as now published after examination under No. 47-19422. Its construction is shown in FIGS. 8(a) and 8(b). As seen from FIGS. 8(a) and 8(b) a sealing plate 5' is provided which includes an enlarged portion 6' made of elastic material around the periphery thereof, and metal core 7' acting as a supplemental part for the sealing plate 5' that includes a folded-over portion 8' around the marginal periphery thereof. When the sealing plate 5' is mounted, it may initially be mounted tentatively or temporarily into a groove 2' provided in the inner or outer race, as shown in FIG. 8 (a). Then, the folded-over edge 8' of the metal core 7' may be forcedly expanded radially outwardly of the sealing plate 5'. This may permit the enlarged portion 6' to be fitted into the groove 2', thereby increasing the amount by which the sealing plate can engage the groove. Thus, the sealing plate may be secured in position. This process is shown in FIG. 8 (b).
As may be understood from the above description, the construction disclosed in the publication referred to above, which is designed to permit the elastic enlarged portion 6' to engage the groove 2', cannot provide force sufficient to retain the sealing plate 5' securely within the groove 2', because the enlarged portion 6' provides a stronger elastic force. In addition, the elastic base material for the enlarged portion 6' may wear during its service life, and the sealing plate 5' may be loosened due to vibrations or any other external forces that may be applied, thereby causing it to lose its sealing function. If any attempt is made to expand the folded-over edge 8' further by force to increase the securing capability of the sealing plate, various types of deformations may occur. For example, the attempt to expand the folded-over edge 8' may increase its diameter which causes a deformation. This deformation may affect other component parts such as the metal core 7'. For this reason, the configuration balance of the sealing plate 5' may be decreased. Particularly, the portions of the sealing plate 5' which are located inwardly of the folded-over edge 8' of the metal core 7' may be insignificantly deformed. Therefore, the configuration precision for those portions may be decreased accordingly. Because of these problems, the construction as disclosed in the above publication cannot be applied as it is proposed therein.
If the metal core 7' does not provide adequate strength to resist forces which tend to significantly expand it, it may easily yield to any stress that may occur when it is being deformed unless a larger space is provided for the mounting shelf 9' on the side on which the rear part of the folded-over edge 8' aduts against it. In this case, the sealing plate 5' may be depressed toward the inner side of the bearing. Thus, the bearing must have constructional restrictions with particular regard to its configuration.